Moment tensor analysis of acoustic emission in concrete specimens failed in four-point bending

Acoustic emission (AE) has been applied extensively to the non-destructive evaluation of materials and structures. In traditional AE measurement, various AE parameters are detected, recorded and analysed to produce information on the characteristics of the material's fracturing behaviour. A quantitative analysis of AE waveforms, known as SiGMA (Simplified Green's Function for Moment Tensor Analysis), can also be used. From this analysis the location of the AE sources can be found and classified into shear or tensile cracks, and their orientations can also be determined. Selection of the initial amplitudes of the P-waves of recorded waveforms enables six independent tensor components to be resolved. To determine source kinematics (crack type and orientation) of a crack, eigenvalues of the moment tensor need to be calculated. This leads to the unified decomposition of the eigenvalues into a shear component, a CLVD (Compensated Linear Vector Dipole) component and a mean component. The aim of the decomposition is to determine the magnitude of shear and tensile contribution of an AE source, thus classifying sources into a crack type. Since the orientations of a shear crack and tensile crack can be determined using eigenvectors, source kinematics can be completely identified from AE waveforms. Notched concrete specimens were failed under a static four-point load. The AE waveforms produced during failure were analysed by the SiGMA procedure. The results demonstrate the ability of moment tensor analysis to determine the location, type and orientation of the crack.